Kohler RH255

Kohler RH255The Kohler RH255 is a 196 cc (12.0 cu·in) natural aspirated single-cylinder four-stroke air-cooled internal combustion small gasoline engine from the 2000/RH series with a horizontal shaft, manufactured by Kohler Co for general-purpose applications.

The cylinder bore and the piston stroke are 68.0 mm (2.70 in) and 54.0 mm (2.1 in), respectively. Compression ratio rating is 8.5:1.

The Kohler RH255 engine produced 5.7 PS (4.2 KW; 5.5 HP) at 3,600 rpm of maximum horsepower and 14.2 Nm (1.45 kg·m; 10.5 ft·lb) at 3,000 rpm of peak torque.

The Kohler RH255 features:

  • OHV design
  • Aluminum cylinder block
  • Cast iron cylinder liners
  • Dependable magneto breakerless ignition system
  • One-barrel carburetor with fixed main jet
  • Automatic compression release
  • Mechanical centrifugal governor
  • High-inertia flywheel
  • Splash type lubrication system
  • Forced air cooling system
  • Recoil or electric (optional) starter

General information

Engine Specifications
Engine modelRH255
Engine type4-stroke, OHV, single-cylinder
Displacement196 cm 3 (12.0 cu-in)
Max. horsepower5.7 PS (4.2 KW; 5.5 HP) at 3,600 rpm
Max. torque14.2 Nm (1.45 kg·m; 10.5 ft·lb) at 3,000 rpm
Cooling systemForced air
Air cleanerReplaceable, dual type
Lubricating systemSplash type
Ignition systemDependable magneto breakerless ignition system
Fuel systemOne-barrel carburetor with fixed main jet
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel tank capacity2.0 liters (2.10 US.qts, 1.75 Imp. qts)
Starting systemRecoil or electric starter
GovernorMechanical centrifugal governor
PTO shaft rotationCounterclockwise (from PTO shaft side)
Dimensions (L x W X H)310x329x325 mm (12.2×12.8×12.8 in)
Dry weight16.0 kg (35.3 lbs)

Cylinder Block and Head

Cylinder block
Compression ratio:8.5:1
Cylinder bore:68.0 mm (2.7 in)
Piston stroke:54.0 mm (2.1 in)
Cylinder internal diameter (standard):68.015-68.030 mm (2.6770-2.6780 in)
Piston skirt outer diameter:67.965-67.985 mm (2.6758-2.6766 in)
Number of piston rings (compression / oil):2/1
Piston pin diameter:17.992-17.995 mm (0.7083-0.7084 in)
Ring side clearance (Top):0.030-0.070 mm (0.0012-0.0028 in)
Ring side clearance (Second):0.020-0.060 mm (0.0008-0.0024 in)
Ring-to-groove side clearance (Oil):0.040-0.200 mm (0.0016-0.0079 in)
Ring end gap (Top):0.147-0.344 mm (0.0058-0.0136 in)
Ring end gap (Second):0.347-0.594 mm (0.0137-0.0234 in)
Ring width (Top):1.470-1.490 mm (0.0579-0.0587 in)
Ring width (Second):1.470-1.490 mm (0.0579-0.0587 in)
Connecting rod small end inner diameter18.010-18.015 mm (0.7090-0.7092 in)
Connecting rod big end inner diameter30.021-30.026 mm (1.1819-1.1821 in)
Main bearing journal outer diameter:24.975-24.989 mm (0.9833-0.9838 in)
Connecting rod journal outer diameter:29.975-29.985 mm (1.1801-1.1805 in)
Cylinder head
Valve arrangement:OHV, gear driven
Valves:2
Valve head diameter (INTAKE):25.000 mm (0.9842 in)
Valve head diameter (EXHAUST):24.000 mm (0.9449 in)
Valve seat angle (INTAKE):89.5-90.0°
Valve seat angle (EXHAUST):89.5-90.0°
Valve face angle (INTAKE):90.0-90.5°
Valve face angle (EXHAUST):90.0-90.5°
Valve steam diameter (INTAKE):5.500 mm (0.2165 in)
Valve steam diameter (EXHAUST):5.500 mm (0.2165 in)
Valve length (INTAKE):64.000 mm (2.5197 in)
Valve length (EXHAUST):62.000 mm (2.4409 in)

Tightening torque specs

Tightening torque specs
Cylinder head (torque in 2 increments) Step 1: 12.0 Nm (1.2 kgf·m; 8.9 ft·lb)
Step 2: 24.0 Nm (2.4 kgf·m; 17.7 ft·lb)
Connecting rod12.0 Nm (1.2 kgf·m; 8.9 ft·lb)
Flywheel74.0 Nm (7.5 kgf·m; 54.6 ft·lb)
Oil drain plug18.0 Nm; (1.8 kg·m; 13.3 ft·lb)
Spark plug27.0 Nm (2.8 kgf·m; 19.9 ft·lb)

Service Data

Valve lash
Intake valve lash0.100 mm (0.0040 in)
Exhaust valve lash0.150 mm (0.0060 in)
Oil system
Lubrication system:Splash type
Oil type:API SJ or higher
Recommended oil:SAE 10W-30, 10W-40
Oil capacity:0.6 liters (0.7 US.qts, 0.58 Imp. qts)
Ignition system
Type:Dependable electronic magneto
Spark plug:Champion RC12YC
Spark plug gap0.76 mm (0.030 in)
Spark plug torque:27.0 Nm (2.75 kg·m; 20.0 lb·ft)
Ignition coil air gap0.254 mm (0.0100 in)

References

1. Kohler 2000, RH series: RH255, RH265 service manual. Kohler Co. 2021.

Author: Sergei Wers
About: Co-founder and CEO of a multi-brand auto repair shop (engine repair, chassis repair, body repair and painting) for over 15 years. I have been developing internet sites with technical specifications for more than seven years.

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We try to use official documentation and verify the published data, but errors may occur. In addition, specifications of machinery and equipment may vary depending on markets and modifications. We do not recommend the use of this data for spare parts or repairs. Use official service manuals or parts catalogs for your product.

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